1. Field of the Invention
The present invention relates to an improved method for the manufacture of the construction material known as "waferboard" or "chipboard" and, more particularly, an improved process for applying release agent to a mass of wood material and binder to facilitate release of the mass from a platen used to compress it during the manufacture of chipboard.
2. Description of the Related Art
Chipboard is a substitute for common plywood. It is manufactured by compressing "chips" or small broken-up pieces of wood material and binder into flat sheets suitable for use in construction. The chips may also be compressed into other shapes useful in construction and other applications. In the manufacture of chipboard, trees are "chipped" or mechanically broken-up into small pieces approximately 1-3 inches in length by 1/4-1 inch in width by 1/32-1/16 inch in thickness. The chips are then mixed with a binder or glue, such as diphenyl methyl diisocyanurate (MDI). A specific volume of chips mixed with MDI is placed on a press where heated, top and bottom platens compress the mass into boards of various dimensions. Both platens are conventionally sprayed with a release agent which prevents the mass of chips and binder from adhering to the hot platens during the compression of the chips and binder. See for example U.S. Pat. Nos. 4,532,096 and 4,374,791.
Spraying the release agent upon the platen, however, is disadvantageous. Aerosolized release agents are sprayed into the atmosphere, thus increasing pollution and possible adverse effects on workers. Moreover, spraying the release agent is not an efficient mode of applying the agent. Significant amounts of the release agent are lost into areas other than the interface of the wafers and the platen.
Numerous other methods of applying release agent are also known. Release agent has been brushed onto the top surface of wood material and binder prior to the step of hot pressing (U.S. Pat. No. 4,201,802). It has been found that utilizing a metallic surface including magnesium and zinc for the platen enhances release of the wood material and binder therefrom (U.S. Pat. No. 4,428,897). Binders having a self-release effect (U.S. Pat. No. 4,528,153) or incorporating an internal release agent are also known (U.S. Pat. Nos. 4,528,153, 4,376,089, 4,528,154, 4,257,995, 4,257,996, 4,376,088 and 4,258,169). See also U.S. Pat. No. 4,110,397 which teaches providing a metallic soap at the interface between the mold and the mass of wood material and binder to assist release.